Generally, bicycle caliper brakes include a pair of brake arms having brake shoes disposed at both sides of a wheel rim, with the brake arms swinging by operation of a control wire, and the brake shoes being brought into press-contact with both side surfaces of wheel rim, thereby exerting the braking action.
Such caliper brake is disposed in the vicinity of the outer periphery of the wheel tire and each brake shoe is spaced at a minute interval from the wheel rim, so that when the wheel is axially deflected by, for example, a collision of the bicycle or a use of the bicycle for motorcross racing on rugged roads, the brake shoes, not during desired braking action, come into contact with the wheel rim, thereby creating a problem of increasing a rotational resistance of the wheel.
Japanese Utility Model Application No. Sho 56-138, 231, discloses a caliper brake wherein the space between the brake shoes is adjustable by means of quick operation. Such caliper brake is so constructed that a holder for a control wire or an outer sheath therefor is supported to a stud movable in the same direction as the movement of the control wire when operated. The stud carries an operating member having a snail-like-shaped cam face spirally extending, and the cam face abuts against a support member supporting the stud, so that the control member is turned to change the position of the cam face in contact with the support member, thereby adjusting the interval between the brake shoes. Hence, in a case where the caliper brake is used especially in a motorcoross bicycle whose body is subjected to a greater impact, the problem is created in that the control member may unexpectedly rotate due to the external force to thereby make it impossible to maintain the carefully adjusted interval between the brake shoes.
The above problem can be solved in such a manner that the cam face of the control member is adapted to contact with the support member at both sides of the path of movement of the control wire, thereby preventing the control member from unexpectedly rotating by the impact on the bicycle. However, in a case where the operating member is hit by an external object during the motocrossing, its unexpected rotation cannot be prevented, and also, the positional relation between the support member and the operating member is restricted to affect a degree of freedom in the design to that extent.